Bone cement compositions are useful in applications such as dental and medical procedures. In particular, they are used in bonding or affixing an implant material to natural bone and to repair damaged natural bone. Although bone cement compositions enjoy wide use in the medical arts, these compositions need to be carefully designed depending on the surgical site at which they will be used. For example, compositions suitable for use in repairing a damaged bone in a limb may not be ideally suited for use in repairing damaged teeth. Similarly, compositions useful in repairing a limb or a tooth may not be ideally suited for surgically repairing the spinal column.
Typically, current bone cement compositions are sold in two-part preparations containing a powder (or dry) part and a liquid (or wet) part, which, when combined, polymerize to form a hardened substance mimicking many of the physical properties of natural bone. The powder part typically includes a polymeric material, such as acrylate polymers, while the liquid part includes a reactive monomer, such as methylmethacrylate. Recent developments have focused on modifying the bone cement composition for particular medical procedures.
For example, to attach prostheses to bone, Faccioli et al. (U.S. Pat. No. 5,004,501) discloses a bone cement composition having a polymer with submicron particle size, i.e. less than 0.9 microns. As stated in Faccioli et al., the function of the submicron particles is to fill any voids left in the bone cement composition to produce stronger bone cement. The patent further discloses the use of fluoride salts to produce a stronger bond between the bone cement and the bone of the patient.
For particular medical applications such as vertebroplasty, manufacturers have turned to producing bone cement compositions having radiopacity and longer setting times. For example, Layergne et al. (U.S. Patent Application No. 2005/0256220) describes a bone cement composition having setting times greater than 15 minutes. In particular, the bone cement is a polymethyl methacrylate (PMMA)-based composition. Layergne et al. achieves a longer setting time using a PMMA-based composition that includes hydroxyapatite and barium sulfate.
In another example of bone cements for vertebroplasty procedures, Voellmicke et al. (U.S. Pat. No. 7,008,433 and U.S. Patent Application No. 2003/0032964) describe a PMMA-based composition to provide radiopacity and further increase the setting time of the bone cement. Specifically, the bone cement composition has a setting time that is at least greater than 18 minutes. To produce a bone cement with a higher setting time and increased radiopacity, Voellmicke et al. use barium sulfate at amounts of 20% by weight to 40% by weight. The barium sulfate particles have D50 sizes of greater than 3 microns and require 50% of the barium sulfate particles to be unbound (i.e. free) from the PMMA particles.
Other applications have focused on increasing the viscosity of the bone cement composition at an accelerated rate to infiltrate the medical site and prevent any migration of the cement during medical procedures. In particular, Beyar et al. (U.S. Patent Application Nos. 2007/0027230 and 2007/0032567), focus on a viscosity greater than 500 Pascal-second at 2 minutes after the initiation of mixing the two components of the bone cement composition. The U.S. patent applications of Beyar et al. achieve a high viscosity at an expedited rate by using one or more sub-population PMMA beads with a molecular weight that is significantly different than a main population of PMMA beads.
Bone cement compositions have been modified to have properties such as longer setting times and high viscosity produced at accelerated speeds. However, these properties are not beneficial for all medical application. Hence, it would be desirable to provide an improved bone cement composition.